The primary objective of this research is the development of new, efficacious, myocardial imaging agents based on the chemistry and nuclear properties of 99m-Tc. This will be accomplished by merging the techniques, equipment and expertise of inorganic chemistry with those of nulear medicine. Emphasis will be on (1) elucidation of the inorganic chemistry of technetium, utilizing the relatively stable isotope 99-Tc and physical techniques such as single crystal X-ray diffraction and thin-layer electrochemistry which require only very small quantities of sample, (2) elucidation of the mechanism of action of existing 99m-Tc myocardial imaging agents, (3) development of synthetic routes to 99m-Tc radiopharmaceuticals that do not involve Sn(II) reduction, and (4) the design and synthesis of new classes of technetium radiopharmaceuticals, the molecular and chemical properties of which can be subtly and systematically modified in order to increase specificity for the myocardium. Animal testing, including the imaging of dogs with induced acute myocardial infarction, will be used to evaluate the efficacy of new radiopharmaceuticals and thereby also provide feedback as to those molecular and chemical properties that enhance myocardial specificity.